Clanker

Don't quit your job till you've passed selection and been given an offer of employment and recieved your dates for Phase 1.
If I were you I'd just wait till your further down the line before considering telling your employer etc.
You want to be 100% that when you leave your job, you'll have another to go into.

Old-Salt

you dont have to leave your job to focus on fitness all it takes is 1.5 hours of training a night. or even just going for a swim after work! i am considering quitting my local gym and taking up just swimming and doing my 1.5 mile runs and enduro runs on the roads.

so yeh dont leave your job. i was made redundant in october and i have a loan and finance and a contract phone to pay . and there are fcuk all jobs around so i am seriously up shit creak with no paddle

Old-Salt

Instead of giving up your job to focus on fitness , try and alter your availability/ shift patterns. So you can plan/work your fitness around it. Like others have said don't give in your notice until you get a "offer of employment" .